Model Based Evaluation of Parallel Hybrid Concepts for a Scooter for Reduced Fuel Consumption and Emissions

Hybrid drive trains have to be cost effective for implementation in small two-wheelers especially scooters which constitute the majority of the market in several Asian countries. Integrating an electric motor with the conventional IC Engine drivetrain while retaining the CVT (Continuously Variable Transmission) is a cost-effective proposition. Such a development will need accounting for the behaviour of the engine, electrical drive and the belt driven CVT. A map-based engine model and a physics-based CVT model were developed in Simulink and validated with experimental data on the WMTC drive-cycle. A steady state map-based emission model and a motor model were also used. Simulations were performed on two parallel hybrid layouts namely P2 wherein the electric motor was placed before the CVT and P3 where the motor was placed in the final drive after the CVT while retaining the base 110 cc scooter powertrain. Both P2 and P3 hybrid layouts consumed 38 and 47% lesser fuel respectively and also emitted lesser HC and CO emissions than the conventional powertrain. The losses in the CVT were higher with P2 hybrid layout. Additionally, the P3 hybrid powertrain will be easier to implement on an existing vehicle as the motor is placed after the CVT and is more preferable. Though the NO_x emission with the hybrid layouts was higher since the engine operated in the more efficient zones it can be curtailed by restricting the maximum operating torque with a small penalty in fuel economy.